This invention relates to an article in the form of a one-piece, hollow member having an enlarged center portion and narrowed or necked down end portions.
More particularly, this invention is directed to forming a hollow, one-piece shaft having an enlarged center portion and necked down end portions from a metal slug. While the following discussion concerns hollow shaft rollers, it is to be understood that this is for convenience only, and that other articles of varying shapes and applications are contemplated by this invention.
Prior to the advent of this invention, hollow roller shafts, as shown in U.S. Pat. Nos. 1,911,171; 2,054,532; 2,283,871; 2,349,898; 2,362,443; 2,647,025; 2,890,933; and 2,926,968, were manufactured by various methods. Principally, these methods involve casting with subsequent machining or forming with subsequent machining. Some involve additional steps of welding and finish machining where individual parts are combined to form the finished roller shaft. The formation of the external dimensions as well as the internal hollow or chamber, frequently internal cavities used as lubricant reservoirs, is costly both in time and materials. In addition, other disadvantages of the prior art include the presence of unrelieved residual stresses in the completed shafts that materially reduce strength and consequent wear life.
It is to an elimination of these disadvantages of the prior art that this invention is directed. The invention provides and an article in the form of a generally cylindrical, hollow roller shaft having an intermediate enlarged portion and being of unitary, one-piece construction formed by a particular method. The method is practiced by beginning with a metal slug and cleaning, coating with lubricant, heating and forming on a press by a series of forming operations. These forming operations include: pre-forming; backward extruding; drawing; re-drawing; nosing and coining. Intermediate steps are provided which include: annealing including local heat application; cleaning and coating.
It is therefore the primary object of this invention to provide a formed, one-piece hollow member having an enlarged center portion.
It is a further object of this invention to provide an article in the form of a formed one-piece hollow roller shaft which has reduced residual stresses and increased wear and resistance to load failure.
It is a further object of this invention to provide a hollow elongated member having an enlarged center portion and narrowed portions at opposite ends thereof.
It is a further object of this invention to provide forming a hollow shaft of one-piece construction having stepped end portions.
It is a further object to provide a hollow reservoir in a one-piece shaft by starting with a solid slug.
It is a still further object to provide a hollow shaft to closely controlled tolerances and having a minimum of inherent residual stress.
Other objects and advantages of the present invention will become apparent upon having reference to the accompanying drawings and the following description.